First of all, for you guys who do not have an idea on what blow-off valve and wastegate is, have you wonder why some car does sound like “psssssttt” when they let go their gas pedal during gear changing, etc? and some even have weirder or cooler sound? blow-off valve or wastegate is the answer for that question. They play around with different type of blow-off valve or wastegate for different purposes.

As for some of you, once you heard that sound you already know that car was a turbocharged car. Or it might be a supercharged car as well. But you might be unaware that the sound was actually produced by the blow-off valve or wastegate.

What are blow-off valve and wastegate? Basically, they were two different devices that do the same job on a forced inducted car. They purge excess pressure that was generated by the compressor to avoid bursting the engine or the forced induction system itself. So, normally a forced inducted car will only have either a blow-off valve or a wastegate. Now we will look further into these two devices.

Many people confused between blow-off valve and wastegate because of their similar task that they perform but actually they works in a different way. The wastegate regulates away exhaust gas from the turbine wheel when a dangerous amount of exhaust gas is detected by a sensor at the inlet of the turbine. This in turn causes the turbo compressor to spin in a limited and controlled speed. In simple words, it was a gate controlled by an actuator to feed in certain amount of air to spin the turbine, hence the name wastegate, a gate which regulates the waste. However there are two types of wastegate, the internal and external:

• Internal : it is a part of the turbo system itself in the turbine housing, regulating the extra exhaust gas back to the exhaust controlled by an actuator.
• External : separated part of a turbo system, regulating the extra exhaust gas back to the exhaust or to the atmosphere and does not requires an actuator. High performance wastegate seeker goes for this type.

Now we see about the blow-off valve. A blow-off valve is installed after the compressor and before the throttle plate. When an engine is pushed hard, logically the compressor generates a lot of compressed air heading towards the engine cylinder. What happens if the driver let off his right foot? The throttle plate will close and thus bounce backs the extremely high-pressured air. This will lead them into the compressor and will cause it to stop spinning or seize!

Thus, by using a blow-off valve, it regulates the extra air out to the atmosphere once the need is detected and this will also keep the compressor spinning happily without the need to spool it up again when the driver accelerates.